Method of removing copper and ammonia from cuprammonium yarn



l atented June 29,1943

METHOD OF REMOVING COPPER AND AM- MONIA FROM CUPBAMIVIONIUM YARN William H. Fumess, Haddonfield, N. 1., assignor to American Rayon Company, Inc., Riverton, N. J., a corporation of New Jersey No Drawing. Application May 1, 1940, Serial No. 332,698

2 Claims.

This invention relates to a method of removing and recovering caustic soda, copper and ammonia-from freshly spun cuprammoniumrayon filaments, films and the like, and its nature, ob- Jects and advantages will be best understood from the following.

The cuprammonium solution may be prepare in any suitable manner, but I prefer to prepare it from wood pulp in accordance with my Patent No. 2,225,431, issued December 1'7, 1940.

The spinning solution is spun into a continuously circulating caustic soda bath, wherein it is set. The bath is relatively dilute and preferably contains from about 25 to about 45 grams per liter of NaOH and possibly more, depending upon such considerations as the concentration of the cellulose in the solution being spun. The bath is fed from a storage tank and the overflow therefrom is conditioned and chemicals are recovered therefrom in the manner described in my copending application Serial No. 332,697, filed November 29, 1939.

Thebundle of filaments (or the-film or the like) leaving the bath, while in a plastic state, is first passed over a device, preferably a preliminary treatment cage, upon which it is laid in the form of a continuously advancing helix. From this preliminary treatment cage the bundle of filaments is passed over a second device, preferabLv a second or main cage, of similar nature,

,in which the filaments are first subjected to a dilute sulphuric acidsolution and then to a water wash and to a drying operation.

The first or preliminary treatment cage is located to one side of the Spinning bath, and the blown up or otherwise directed against the cage from below.

The hot water removes the bulk of the caustic soda and practically all of the ammonia from the copper in the filaments is thus removed as cupric hydroxide. I

The wash liquor, containing caustic soda, ammonia and cupric hydroxide (and some sodium sulphate), is collected in a suitable pan beneath the cage and is led to a series of settling'tanks in which the cupric hydroxide has an opportunity to settle out for removal. (It may, alternatively,

be otherwise removed as by centrifuging, filter ing or the like.) This cupric hydroxide, washed to free it 0! caustic soda, may be utilized to neutralize free acid in the acid wash liquors from the main cage and to convert the copper sulphate in such liquors into basic copper sulphate, for ultimate conversion of the basiccoppersulphate into tetrammonio copper sulphate and copper hydroxide, as described in my copending application Serial No. 332,696, filed May 1, 1940.

From the last settling tank the liquor freed from the bulk of tlis cupric hydroxide, and now containing caustic soda, sodium sulphate, ammonia and a very small amount of cupric hydroxide, is passed through a heater where it is boiled. This drives of! ammonia as gas, which hereinbefore described. It also I heater or boiler where the heating is continued until sufllcient water is driven off to bring the concentration of the caustic soda to such a point that the concentrated liquor may be returned to the storage tank of the setting bath.

This heating removes water from the system which was introduced by the hot water wash converts any residual cupric hydroxide into the black copper oxide, which precipitates (as in a settling tank) is drawn of! and washed to free it of caustic soda and is reused in the system as hereinafter described. (It may be otherwise separatedin ways hereinbefore indicated.)

The concentrated caustic soda liquor, on its way to the storage tank, is cooled, which causes filaments. Some of the copper in the filaments is present, probably as cupric hydroxide, due to the action of the caustic soda of the setting bath. This is, as it were, in solution in the ammonia present in the filaments..- The water not only drives cit some of the ammonia as vapor but progressively dilutes the remaining ammonia, so that the copper can no longer stay in solution but tends to come out. The continued application of the water washes of! the ammonia and the the sodium sulphate therein to crystallize out. This has the effect of further increasing the con centration of the caustic soda in the liquor because the" sodium sulphate, in .crystallizing out, removes a substantial amount of water. The amount of water boiled oil! and removed as water of crystaliizationis preferably such as to bring the concentrationof NaOH-in the remaining liquors to the desiredpoint.

The ammonia and'steam driven off in the first boiler are condensed to ammonia water and used cupric hydroxide. A substantial portion of the in the conversion of ammonium sulphate into and recovered for use by concentration.

tetrammonio copper sulphate, as will now be described.-

When the hot water is applied to thelfirst' cage, the ammonia which is driven oil. as gas is' exhausted from the housing enclosing the cage,

and, along with air, is delivered to a coke-filled or other absorption tower to which dilute sulphuric acid is likewise delivered and from which the air escapes. In trickling down, there is formed ammonium sulphate which flows into a vessel where itcrystallizes and can' from time to time be withdrawn. Ammonia and cupric hydroxide are now added to the ammonium sulphate and the reaction is which is copper tetrammonio sulphate, utilized in preparing fresh cellulosic spinning solution.

. It will thus be seen that- I have provided a very simple and inexpensive method for efiec'tive- 1y removing and recovering ammonia, copper and caustic soda in freshly spun filaments, films or ration and condensation, and .the condensed water may, for example,'be utilized as the or part of thewash water employed in the hot water wash section. I

Instead of a hot water wash, I may use a cold water wash, but I pfcfer the hot water because caustic soda .is more soluble therein and it is therefore possible to'remove a larger quantity of causticsoda from the filaments with a given "amount of water. "Likewise the use or hot water ensures the removal of practically all of the ammonia from the filaments. It is desirable to have practically all the ammonia removed from the filaments before they are subjected to the sulphuric acid wash in order to avoid the presence of substantial amounts of ammonium sulphate in the acid wash liquor, as this would interfere with the recovery of copper sulphate as basic copper sulphate by the use of cupric hydroxide, and the ultimate conversion of the basic copper sulphate into tetrammonio copper sulpate and copper by- *droxide. The temperature of 'the hot water should be sufiicient. to accomplish the end sought,

but preferably not so high as to convert the cupric hydroxide into the black copper oxide.

The present invention is useful in thecomplete system described in my copending application, Serial "No. 332,694, filed May 1940; but since it is capable of and useful in independent use, I herein claim it separately.

What I claim is:

1. In the cuprammonium process of spinning.

rayons, films or the like, in which a caustic soda spinning bath of;predetermined concentration is employed, the process of recovering the caustic 15 soda from the freshly spun material as a caustic soda solution fit for -re-use, which comprises subjecting the freshly spun material after leaving the setting bath and while in a plastic state to a water wash to remove causticsoda, ammonia 20 and copper, collecting the wash liquor and separating therefrom the cupric hydroxide precipitated by the dilution of the ammonia present, heating the remaining liquor containing caustic soda, ammonia and copper hydroxide to evapo-' 25 rate waterand any ammonia present, further- \heating the liquor until the concentration of caustic soda therein approximately reaches said predetermined concentration, separating the black copper oxide produced from the copper hydroxide by the heating, and returning the con-' centrated caustic soda solution to the spinning bath.

2. In the-cuprammonium process of spinning rayon, films or the like, in which a caustic soda spinning bath of predetermined concentration is employed, the process of recovering the caustic soda from the'freshly spun material as a caustic soda solution fit for re-use, which comprises sub- 'Jecting' the freshly spun material after leaving the setting bath andwhile in a plastic state to a water wash to remove caustic soda, ammonia and copper, collecting the wash liquor, heating the liquor so collected and containing caustic soda, ammonia and copper hydroxid to etaporate water and any ammonia present until the concentration of caustic soda therein approximately reaches said predetermined concentration, separating the black copper oxide produced from the copper hydroxide by the heating, and returning the concentrated caustic soda solution to the spinnin bath.

WILLIAM H. FURNESS. 

